Smart material actuators provide very scalable actuation properties due to the inherent solid state nature of the actuation force and displacement. However, they also exhibit many limitations and challenges due to the non-linear and field-dependant nature of the force and displacement generation. For example, they can be hard to precisely control, often require continuous power draw to hold position, experience stroke and force decay over lifetimes, and can be damaged when excessively loaded.
One approach to mitigate all of these limitations is to use active materials in combination with another mechanical structure that together provide the necessary functionality.
Bistable Actuator devices are combinations of a bistable mechanism and an actuator to switch the mechanism from one stable state to another. Such devices, while known in the art, suffer from various problems depending on the design. Some designs do not provide a well controlled displacement trajectory, such as a one-dimensional motion, that is desired for a particular application. Some designs are not scalable in that there is an upper or lower limit to the physical size of the device. Others have limited range of motion or a limited ability to exert a force.
For example, SHAPE MEMORY ACTUATOR WITH BI-STABLE OPERATION (U.S. Pat. No. 6,762,669) focuses on mechanistic implementations of bistability that are not scalable due to the use of pivots, pins, springs, mechanical hinges, etc. In addition, achieving a state depends on a spring stretching the shape memory actuator while achieving the alternate state requires the shape memory actuator overcoming the spring. In effect, the operation of the device depends on a balance between the shape memory actuator and the spring, thereby limiting the design options. Other implementations are focused on sensor implementation, such as a thermostat or other temperature sensor, and do not provide the actuation functionality disclosed herein.
U.S. Pat. No. 7,411,331 discloses a concept limited to dielectric elastomer actuation. Such an approach is limited in the range of motion and or the force available. Moreover, the actuation method requires the presence of an energy source to maintain a particular configuration.
As such, there is a need for Bistable Actuation devices that have a large range of travel, can maintain a particular configuration without consuming energy and is scalable.